The invention relates generally to a turbomachine such as a gas turbine, and more particularly, to an assembly and method for attaching a rotating turbine blade to a rotor wheel.
Rotating blades in turbomachines such as gas turbines are typically subjected to extremely high temperatures during operation. In the past, blades and other features have been made of metals such as high temperature steels and nickel alloys. These metal blades have required the addition of cooling passages in order to prevent the blades from melting and deforming during operation. Alternatives to the engineering difficulties presented by the cooling requirements of metal blades have included the use of ceramic coatings on metal blades, and the use of entirely non-metal blades made of, e.g., ceramic. Ceramic blades provide additional advantages, such as lighter weights which result in greater efficiency in the turbomachine.
Conventional joints between metal blades and rotor wheels have used a fir tree attachment or root design, having multiple tangs or surfaces. For example, a three tang design may be used. In contrast, ceramic blades have typically used a dovetail design having a single tang, an arrangement less prone to wear and breakage in ceramic blades due to thermal mismatch between the metal wheel and the ceramic blade. Despite the advantages of equipping turbomachines with non-metallic blades, the non-complementary shapes of non-metallic blade dovetails and rotor wheels designed to accept metal blades having a fir tree attachment member present a challenge in doing so.